The production of wrought refractory metal products containing minor quantities of a desirable alloy is well known in the art of consumable metal electrode technology. Generally, a rod or electrode of a desired starting material is electrically isolated in a holder and positioned within a reservoir capable of withstanding the elevated thermal conditions known to be associated with arc melting. A cathode source or spur is located at the base of the reservoir so that when a voltage is applied to the electrode from an exterior power supply, an electrical discharge occurs which travels between the ground source and the anode at the nose portion of the electrode body. The heat from the arcing induces melting of the electrode which in turn falls into the reservoir or crucible. After the molten pool cools, it is processed into a wrought product.
Where it is desired to alloy additional metals to the starting metal, it is known to add patches of alloyed metal as disclosed in U.S. Pat. No. 3,933,474 or to weld strips of metal to the body 10 as disclosed in U.S. Pat. No. 4,481,030. Alternately, a variety of metal bodies may be used each composed of a desired starting metal. See for example U.S. Pat. No. 2,958,913. Where the alloy is attached to the electrode periphery in a manner which raises the alloy above the periphery of the electrode to form a protrusion, arcing frequently occurs from this point to the walls of the reservoir. Alternatively, alloy strips which are recessed flush with the periphery also suffer from the same problem due to the lower resistivity of the alloy presenting a pathway of least resistance to ground. Where the alloy is in the form of welded strips, the arcing frequently travels up the side of the electrode resulting in discontinuous heating of the pooled metal and spraying of the starting metal onto the walls of the crucible. Damage to the reservoir wall and non uniform melting of the electrode body often is characteristic of these methods.
Another problem inherent in these prior art methods is that arcing to the crucible walls also introduces contaminants from the wall melt into the ingot.
A further problem inherent in these prior art method is that as the melting process is non uniform, the melt cycle is stopped short of consuming the full electrode body. A non uniform melting of the electrode therefore requires the use of larger quantities of starting material to insure the formation of a desired ingot weight.
Various attempts have been made at delivering secondary materials into the melt by spray coating. See U.S. Pat. No. 3,271,828 which discloses spray coating flux onto the electrode body.
Other attempts have placed the desired alloy material centrally within an axial core in the electrode body surrounded by the starting metal. See U.S. Pat. No. 1,085,951.
None of these prior attempts have managed to control the arc sufficiently to result in uniform melting of the electrode body or to achieve a uniform distribution of minimal quantities of alloy within a larger quantity of starting metal.
One object of the present invention is to uniformly distribute a desired quantity of alloy within a larger quantity of starting metal simultaneous with the consumable electrode body melt.
Another object of the present invention is to provide a smooth electrode body arcing-surface which is free from protrusions and which minimizes arcing to the side walls of the crucible.
Yet a further object of the present invention is to provide a means for mixing the molten alloy with the molten starting material without adding crucible contaminants to the molten pool. A process which addresses these problems would be a significant advancement in the art of producing alloyed wrought product.